Estimated Wh/mi?

I searched and did not locate a similar topic. I am disappointed that the RESTful API does not provide access to the Wh/mi values that show up on the console. Thinking about this got me wondering if it is possible to synthesize or approximate those values via rated vs. projected range. At first thought it seems reasonable to assume that (Rated Range / Projected Range) is approximately (Actual Wh/mi / Rated Wh/mi). Am I missing something obvious?